LIBRARY

HEMIPTERA 265
of living plants, causing great losses to agricultural crops. They not only
destroy the plants by excessive feeding but inject into the tissues toxins and
virus diseases that are often very destructive to plant life.
A considerable number are predacious upon many small animals and other
insects, and attack warm-blooded birds and mammals, including man. These
forms may also transmit organisms that cause diseases and death to the hosts.
The oldest fossil ancestors of the HEMIPTERA are the members of the
order PROTO HEMIPTERA Handlirsch characterized by small head. pronotal
expansions, suctorial mouth parts, and complicated, netted wing venation.
The genera Eugereon Dohrn from the Lower Pennian of Germany and
Mesotitan Tillyard from Middle and Upper Trias of New South Wales, Australia,
are among the largest fossil insects known, the former having an estimated
wing expanse of 160 mm.
In the Lower Permian of Kansas the homopterous members of the archaic
family ARCHESCYTINIDlE occur. In wing venation these ancestors are
also allied to the PSOCOPTERA (Imms, 1937). In the Upper Permian of
Belmont, Australia, homopterous forms of the family SCYTINOPTERIDJE
Handlirsch were found. The latter family and the family PROBOLIDJE were
also taken in Russia by Martynov (1928). HETEROPTERA appear in the
Trias at Ipswich, New South Wales, in the families DUNSTANIIDlE, related
to the PENTATOMIDlE, and TRIASSOCORIDlE, having affinities with the
NOTONECTIDlE. In the Trias of Australia the HOMOPTERA were also
represented by the MESOGEREONID)E, ancestors of the CICADIDJE.
(Tillyard, 1926).
In the Jurassic remains they are quite common, and in the sediments and
amber of the Tertiary they are often abundant.
The HEMIPTERA is a relatively large order consisting of approximately
150 families, 1,000 genera, and 48,000 species. The members occur throughout
the world except in the polar areas. Members of certain families are most
abundant in the tropics, while others reach their greatest development in the
temperate regions. Individuals of a given species of HOMOPTERA may
attain inconceivable numbers and overrun the food plants in a small or large
area.
KEY TO SUBORDERS
1. Base of rostrum usually not touching anterior coxre; gular region 1 usually
well developed, long; pronotum large; fore wings usually thick·
ened basally and membranous apically, hind wings membranous, both
pairs folded flat over the back with apices overlapping; tarsi normally
three-segmented . . HETEROPTERA p. 266
2. Base of rostrum usually touching anterior coxre; gular region wanting,
short; or membranous; pronotum small; wings usually of same texture
throughout (the fore pair rarely thickened and pigmented in CICA­
DELLIDlE. folded roof-like over the back; tarsi one- to threesegmented.
. HOMOPTERA p.307
1 Snodgrass (1935) calls this the hypostomal bridge.